4-Switch - Start Up Issue / Glitch

[Hank Rearden]

What can be causing this? I made a video explaining what I've done to the unit so far.

 

https://youtu.be/jEkv09a0MJQ

 

At 3:26 is when I demo the problem I need solved?

 

I've replaced all the caps (201, 214, 241, 242, 243), the voltage regulator (A203), the 3.579545 MHZ Crystal, completely removed the RF, added the 820 ohm resistor to pins 6 & 9 of the TIA, and inserted a composite modification kit.

 

What can be causing my start up issue and why the sound issue on Pitfall?

[+DrVenkman]

Have you tried swapping any of the ICs with a working unit?

[Hank Rearden]

Have you tried swapping any of the ICs with a working unit?

You know what's funny. I've been debating doing that on a Commodore 64 I have that isn't running but I've been afraid of doing harm to anything in my fully functional, seriously like new unit. That's a project for another day.

 

I'm such a dummy and never thought of trying that on the Atari! I only have 3 of them. LOL

 

So far I've swapped the TIA's (the chip at the bottom) and that seems to have fixed sound problem on Pitfall. When I put the faulty chip in the unit that's been running fine, I have the same sound issue. So one of my mysteries is solved. I have a bad TIA, although, the only thing it seems to harm is the sound on Pitfall. I haven't noticed anything wrong in any other games but that could be because I'm not always aware of what is always supposed to happen. Regardless, it seems that chip is faulty.

 

However, I still seem to have the powering on issue. Now I'll get either the vertical color bars or a streaky screen with the high pitched whine. I guess I'll swap the other chips as well and see what happens.

[Hank Rearden]

Have you tried swapping any of the ICs with a working unit?

Thank you DrVenkman! Swapping the TIA and the middle CPU chip seems to have moved all issues from one unit to the other. It just may be another Scooby Doo mystery has been solved!

 

While the faulty symptoms don't seem to repeat nearly as much in the RF unit, they are there and do occur. However, they seem to be gone in the the composite upgrade unit. All I need to do now is get some replacement chips and I'll have 3 fully functional units!

 

I need to do a little more play testing to be completely certain but I think I'm finally on the right path.

 

If you or anyone else reading this might have some understanding as to why those chips would cause those problems, I would love to have a better understanding.

 

I truly appreciate all advice I've received on these boards to date! I'll do my best to reciprocate where I can.

[Keatah]

To be more definitive and certain you'd need to connect them to a logic analyzer. The middle one is like a 5000 transistor CPU. Any one of those microscopic parts could've gone bad.

[Hank Rearden]

To be more definitive and certain you'd need to connect them to a logic analyzer. The middle one is like a 5000 transistor CPU. Any one of those microscopic parts could've gone bad.

That isn't something I have access to unfortunately. Is that the only chip you can test that way or would that hold true for pretty much any chip? I saw something about using a Harmony cartridge but the picture I saw had wires running everywhere and appears to be out of my scope.

 

Which leaves me with a chip swapping method of at least narrowing down the symptoms to a specific chip or chips in this case.

 

It was really strange how the only thing that I noticed the TIA was doing was messing with the sound on Pitfall.

[Keatah]

Some smaller 8 and 16 pin chips you can test with a logic probe or a scope. It really depends on their function. Basic logic gates are easy to test. Memory chips in that size, not so much.

 

It was really strange how the only thing that I noticed the TIA was doing was messing with the sound on Pitfall.

 

Not unusual. It's just a corner case. I bet there are other games that'd mess up if you took the time to go through every single game in the VCS' library.